Th1 refers to the first thoracic spinal segment.

• Situated between cervical segment C8 and thoracic segment T2
• Corresponds approximately to the first thoracic vertebra (T1)

• Origin of spinal nerves T1, which contribute to:
  • Brachial plexus (particularly the inferior trunk)
  • Sympathetic preganglionic neurons in the intermediolateral cell column (IML)
• Part of the thoracolumbar outflow of the sympathetic nervous system

• Lesions at Th1 may cause:
  • Horner syndrome (ptosis, miosis, anhidrosis) due to disruption of sympathetic fibers
  • Motor or sensory deficits in the medial arm/forearm

Th1 cells are a subtype of CD4+ T helper lymphocytes that orchestrate the cell-mediated immune response.

• Activate macrophages and cytotoxic T cells
• Promote defense against intracellular pathogens (e.g., viruses, some bacteria)

• Secrete Interferon-gamma (IFN-γ), IL-2, TNF-α
• Stimulated by IL-12 (from dendritic cells/macrophages)

• Th1 dominance is associated with:
  • Autoimmune diseases (e.g., type 1 diabetes, multiple sclerosis)
  • Resistance to tuberculosis
• Imbalance between Th1/Th2 responses affects immunity and hypersensitivity patterns

• thoracic_spinal_cord
• thoracolumbar_outflow
• t_helper_cells